A nano-imprint method having resolution not restricted by the limits of conventional machining and photolithography attracts attention as a method for forming a micro three-dimensional structure.
For example, U.S. Pat. No. 5,772,905 discloses the following nano-imprint method. As described below, first, a substrate on a surface of which a thin film of a thermoplastic resin such as polymethyl methacrylate (PMMA) or the like is formed, and a mold on which a micro recess/projection pattern is formed are prepared. Next, the mold is pressed on the thermoplastic resin softened by heating the substrate to the glass transition temperature or more. Then, the mold is released from the thermoplastic resin solidified by cooling to the glass transition temperature or less. Consequently, a reverse pattern of the micro pattern of the mold is formed in the thermoplastic resin.
On the other hand, as a nano-imprint method using a substrate on a surface of which a thin film of active energy ray-curable resin is formed, Japanese Patent Laid-Open No. 2000-194142 discloses the following method. For example, a mold composed of an active energy ray-transmitting material, such as quartz or the like, and having a micro recess/projection pattern formed thereon is prepared. Next, the mold is pressed on the active energy ray-curable resin layer formed on the substrate, active energy rays are applied through the substrate to cure the active energy ray-curable resin, and then the mold is released. Consequently, a reverse pattern of the micro pattern of the mold is formed in the active energy ray-curable resin layer.
As described above, the nano-imprint method requires preparation of a mold on which a desired pattern is formed. Methods for forming the mold include a method of forming a silicon, Ni, or quartz mold using exposure and development technique, and etching technique, and the like.
However, in order to prepare a micro three-dimensional structure mold having a plurality of steps, it is necessary to repeat etching. Therefore, it is difficult to keep the depth and height of a recess/projection pattern constant and maintain the shape of an edge, and when quartz which is an active energy ray-transmitting material is used, it is difficult to prepare a mold with high precision because micro trenches occur.
Therefore, there is a conceivable method for forming a micro three-dimensional structure by a plurality of times of pressing using a plurality of molds each having one-step projections. However, a thermal imprint method as in the above Patent Literature 1 requires a high-temperature press process. Therefore, when a substrate having a certain pattern formed thereon is again heated to the glass transition temperature or more and pressed, the pattern formed in a thermoplastic resin by pressing is softened, thereby failing to maintain the shape. Therefore, in the thermal imprint method, it is difficult to form a micro three-dimensional structure with high precision by a plurality of times of pressing using a plurality of molds.
On the other hand, as a non-heating pressing method, U.S. Pat. No. 6,818,139 discloses a method in which a porous structure is formed in a thermoplastic resin on a substrate, and imprinting is performed at the glass transition temperature or less.
As described above, as a non-heating method for forming a micro three-dimensional structure by a plurality of times of pressing using a plurality of molds each including one-step projections, there is a known method in which a porous structure is formed in a thermoplastic resin on a substrate, and imprinting is performed at the glass transition temperature or less. However, when this method is used, the porous material decreases at each time of pressing, and thus pressing force is not absorbed and the influence on the periphery of a pattern to be pressed cannot be neglected, thereby possibly breaking the pattern pressed in the thermoplastic resin.
Therefore, in a room-temperature imprint method using a thermoplastic resin having a porous structure formed therein, it is difficult to form a micro three-dimensional structure by a plurality of times of pressing using a plurality of molds.